Inverters have been used in a wide variety of applications to convert a direct current (DC) energy source to an alternating current (AC) energy source. One such application involves using an inverter within an electric or hybrid-electric vehicle to convert DC power to AC power, which is applied to an electric motor for traction. Inverters that provide power for traction are sometimes described as traction inverters.
A typical inverter topology for converting DC power to AC power includes one or more inverter switches and diodes, which are switched on and off with respect to each other to yield an AC power output. Inverters used in high power and high temperature applications, such as traction inverters, have employed wide bandgap (“WBG”) semi-conductors for the inverter switches and diodes. WBG semi-conductors are often utilized in high power and high temperature configurations because of their low thermal resistance, which allows for improved cooling.
In order to model the power dissipation in the electronic components in an inverter, steady-state power dissipation equations have been developed by Oak Ridge National Laboratory National Transportation Research Center for Si and SiC semi-conductor devices, a type of WBG semi-conductor, currently used in traction inverters for hybrid-electric vehicles. The power dissipation in the devices may be a function of the electrical resistance based on junction temperature, applied current, and applied voltage. The study revealed that despite the improved cooling characteristics of WBG semi-conductors, conventional inverters may be exceeding the operating parameters, such as temperature, of the WBG semiconductors. Cooling strategies such as direct cooling with air or indirect cooling with liquid have been used in conventional inverters.
Direct cooling an inverter with air involves passing air directly over thermal energy sources, such as the packaged inverter semi-conductors. Exposure to the main flow of the coolant may create a risk of dielectric breakdown that could cause a short circuit due to accumulation of matter (e.g., dust) on the thermal energy sources and their associated DBC traces.
Indirect liquid-cooled inverters use a silicone gel to protect the sensitive power electronic devices, such as the inverter semi-conductors and their connections, from direct contact with the liquid. A drawback of a liquid-cooled system is that there is a potential for coolant leaks, which result in the electrical connections being shorted. Further, there is the added complexity, cost, space, and power consumption of the liquid-cooling system. Lastly, using silicone gel over the power electronics may prevent direct cooling.
Accordingly, there remains a need for an improved system and method for cooling inverter circuitry. In particular, there remains a need for an improved system and method for gas cooling inverter cards.